Ovens for cooking and baking food have been known and used for thousands of years. Basically, oven types can be categorized in four different forms. The simplest and probably the oldest cooking resulted when man put some vegetable or grain products on a hot rock next to a fire, and cooked them essentially by the heat transfer method of conduction. With a little more refinement, an enclosure surrounding the heating element entrapped the heated air giving rise to cooking by convective heat transfer. This was the prototype for the modern gas or electric oven. In the past century, radiant energy from infra-red radiation sources has been used to heat and cook foodstuffs directly. Within the past few decades, microwave radiation has proved useful in allowing very short cooking times for many types of food.
There are subtle differences between cooking and baking. Cooking just requires the heating of the food. Baking of a product from a dough, such as bread, cake, crust, or pastry, requires not only heating of the product throughout but also a chemical reaction coupled with driving the water from the dough in a predetermined fashion to achieve the correct consistency of the final product and finally browning the outside. Following a recipe when baking is very important. An attempt to decrease the baking time in a conventional oven by increasing the temperature results in a damaged or destroyed product.
It has generally been believed that radiation with wavelengths much shorter than 1 .mu.m is not of much value in cooking or baking processes, partly because of the weaker interaction of the shorter wavelengths with the foodstuff molecules in terms of general heat transfer, and partly due to the inferior penetrating properties of such radiation. In particular, it has seemed that visible light, i.e., radiation with a wavelength in the range of 0.4 to 0.7 .mu.m, is not very useful in the cooking process. However, if one provides a sufficiently intense source of visible light radiation in conjunction with infra-red radiation, a novel and very effective cooking apparatus results. The combination of the deeply penetrating infra-red and the intense visible radiations establishes a temperature gradient within the interior of the foodstuff. This strong gradient created by the differential absorption of the infra-red and visible radiations ensures that the surface temperature of the foodstuff is hotter than the interior, and the products of the cooking, i.e., the water vapor and gases like CO.sub.2, are quickly driven to the surface and out of the foodstuff. This process results in a very rapid cooking of the foodstuff.
Using intense visible and infra-red radiation to cook food has a number of significant advantages. First of all, the cooking process is very fast. Bakery products, like pizza crust for example, can be baked 5 to 10 times faster than ovens that use only infra-red energy or rely on conventional convection and conduction processes. Secondly, the quality of the cooking process is enhanced for many foodstuffs. For example, crusts become fully cooked with crispy exteriors and moist, chewy interiors. Vegetables are cooked so fast that they are virtually steamed in their own water vapor, leaving them hot, but with very little loss of any of their nutritive values.
In general, this is a new mode of cooking. The potentialities of using this enhanced range of wavelengths for cooking and baking are just starting to be explored, and a whole new range of cooking techniques should result from the invention.